Treatment with streptococcal preparation (OK-432) suppresses anti-islet autoimmunity and prevents diabetes in BB rats.

We have recently shown that a streptococcal preparation (OK-432) inhibits insulitis and prevents diabetes in nonobese diabetic (NOD) mice, an animal model of insulin-dependent diabetes mellitus (IDDM). We extended this study to another model of IDDM, namely BB rats. Male and female BB rats were injected weekly with 0.2 mg OK-432 i.p. starting from 5 to 6 wk and continuing through 20 or 30 wk of age. The cumulative incidence of IDDM over 20 wk in the OK-432-treated BB rats (4 of 54, 7.4%) was significantly (P less than .01) lower than that found in the nontreated BB rats (13 of 47, 27.7%). We examined some of these rats as follows. All of the OK-432-treated BB rats tested showed normal glucose levels before and after oral glucose administrations, as did the nontreated and nondiabetic BB rats. Histological examination of pancreatic sections revealed that the OK-432-treated rats retained a greater number of intact islets without infiltration of the mononuclear cells than did the nontreated BB rats. A preliminary in vitro study further demonstrated that the cytotoxic activities of spleen cells against a rat insulinoma cell line, RIN, were suppressed in the OK-432-treated rat. However, the treatment of BB rats with OK-432 showed no suppressive effects in the spleen cell number, the responsiveness of spleen cells to concanavalin A, the populations of OX19+, W3/25+, and OX8+ peripheral blood lymphocytes, or in the titers of cell surface antibody against RIN. These results suggest that a nonimmunosuppressive immunomodulator such as OK-432 may be useful as an agent for immunotherapy of IDDM.